1. Field of the Invention
The present invention relates to a seal hardening furnace of a liquid crystal display device, and particularly, to a structure of a rack bar within a seal hardening furnace.
2. Description of the Related Art
In general, a liquid crystal display device includes a liquid crystal display panel having unit pixels formed thereon in a matrix configuration, a driving circuit unit for supplying a scanning signal and an image signal to the liquid crystal display panel, and a back-light unit for supplying light to the liquid crystal display panel.
In particular, the liquid crystal display panel is equipped with an upper color filter substrate, a lower array substrate, and a liquid crystal layer filled in a position between the two substrates. The two substrates, namely, the color filter substrate and the array substrate are attached to each other by seal lines formed at their edges.
Hereinafter, a process for fabricating the liquid crystal display panel will briefly be described. The process for fabricating the liquid crystal display panel includes forming the array substrate on which a thin film transistor used as a switching device is formed; forming the color filter substrate on which a color filter layer for rendering information with color; forming seal lines on one certain substrate of the two substrates; attaching the two substrates by the seal lines; and cutting the attached substrates into unit liquid crystal display panels. The liquid crystal layer may be formed after performing the cutting process when adopting an injecting method. Otherwise, the process for forming the liquid crystal layer may be carried out at the same time as the attaching process is ongoing when adopting a dispensing method.
In general, a plurality of liquid crystal display panels are formed on a mother substrate so as to improve productivity. When a plurality of array substrates and color filter substrates are formed on one mother substrate, one of the two substrates is coated by a sealant which is made of thermosetting resin to thereafter heat up for attaching an upper substrate (the color filter substrate) and a lower substrate (the array substrate).
The process for attaching the upper substrate and the lower substrate of the liquid crystal display panel will now be explained in more detail with reference to FIGS. 1A and 1B.
As shown in FIGS. 1A and 1B, the array substrate and the color filter substrate are substantially attached by heating them within a chamber 10, using an attaching device.
When the array substrate and the color filter substrate are completely formed, seal lines are formed at edges of one of the two substrates. Thereafter, as shown in FIG. 1A, an upper substrate 8b and a lower substrate 8a of the liquid crystal display panel are fixed, respectively, to a lower stage 2 and an upper stage 4 within the chamber 10.
After fixing the two substrates, the upper stage 4 descends to thereby provide a uniform pressure on the lower substrate 8a. At this time, the upper substrate 8b and the lower substrate 8a are attached to each other by the seal lines due to the provided pressure.
The attaching process is carried out within a chamber 10 which is heated up to a certain temperature. However, after completing the attaching process, the substrate undergoes a hardening process. While hardening it, a pressure in an inner space of the liquid crystal display panel which is formed by the attachment is different from an air pressure of the hardening chamber. As a result, the pressure acts upon the seal lines so as to make holes in the seal lines.
Therefore, in order to temporarily harden the seal lines during the attaching process, a UV (Ultra-Violet) hardening process for irradiating the UV radiation on the seal lines is carried out. Hence, the chamber in which the attaching process is performed is further provided with a UV lamp for generating the UV radiation.
Accordingly, after completely carrying out the attaching process within the chamber 10, a primary hardening for the seal lines by the UV radiation is performed.
Afterwards, a secondary hardening for the liquid crystal display panel for which the primary hardening has been performed is carried out in a seal hardening furnace, thereby completing the attaching process. The second seal hardening is performed in a separate chamber from the chamber in which the primary hardening is performed.
The secondary hardening is substantially carried out within the chamber for a predetermined time in a heated state. The chamber has a cassette therein which is equipped with a rack bar, so that the seal hardening for the plurality of substrates can be performed.
With reference to FIGS. 2A and 2B, structures of the cassette and the rack bar within the chamber in which the seal hardening is carried out will now be described. FIG. 2A is a perspective view illustrating a cassette within a related art seal hardening furnace and FIG. 2B is a front view thereof.
With reference to FIGS. 2A and 2B, a cassette 200 within a seal hardening furnace (not shown) is composed of a plurality of layers for placing a plurality of substrates 204 thereon. A plurality of rack bars 201 for supporting the substrate (not shown) is installed on each layer in a Y axis direction thereof, and a rack bar support 202 for supporting the rack bars 201 is installed on a front end of the rack bar 201 in an X axis direction on each layer. Therefore, the front end of the rack bar 201 is positioned on an upper surface of the rack bar support 202, and a rear end thereof is installed on a rear surface of the cassette 200 and fixed by a second rack bar support 205 which is installed in a Z axis direction.
The rack bars 201 have certain heights and are installed with a certain interval to thereby support the substrate loaded thereon. Accordingly, uniform spaces 203 are formed between the rack bars 201 adjacent to each other, and fingers 206 of a robot arm are introduced into and drawn out through the spaces 203 to load and unload the substrate.
However, in order to harden the seal lines formed of thermosetting resin, the substrate is typically placed in the seal hardening furnace for a long time in a high temperature state. At this time, stain is generated on the substrate region in contact with the rack bars 201, which causes defects in the liquid crystal display panel.
In particular, due to the large-size liquid crystal display panel being heavy, a more substantial amount of strain may be generated in the region where the substrate contacts the rack bars 201.